Plasma-derived therapeutic proteins, unlike other biologics that are produced via recombinant expression of DNA vectors in host cell lines, are fractionated from human blood and plasma donations. The supply of these plasma-derived products cannot be increased by simply increasing the volume of production. Rather, the level of commercially available blood products is limited by the available supply of blood and plasma donations. This dynamic results in a shortage in the availability of raw human plasma for the manufacture of plasma-derived blood factors that have lesser established commercial markets, including Factor H (FH).
Factor H is a large (155 kDa), soluble glycoprotein that functions in the regulation of the complement Alternative Pathway to ensuring that the complement system acts on pathogens and not host tissue. Factor H circulates in human plasma at a concentration of 500-800 micrograms per milliliter, binding to specific glycosaminoglycans (GAGs) present on human, but not most pathogenic, cell surfaces. Once located to self-cells and tissues, Factor H down-regulates complement activation through Factor I cofactor activity of C3b cleavage and decay accelerating activity against the alternative pathway C3 convertase, C3bBb.
Factor H is implicated as a potential therapeutic agent for several human disease states, including age-related macular degeneration (AMD), hemolytic uremic syndrome (aHUS) and membranoproliferative glomerulonephritis (MPGN). However, because of the extremely high worldwide demand for plasma-derived pooled immunoglobulin G (IgG), source plasma is not readily available for the direct isolation of Factor H. Rather, methods for Factor H isolation that can be introduced into existing IgG manufacturing schemes are needed. Several methods have been suggested to achieve just this, however, many of these proposed solutions require modification of the existing manufacturing scheme for established products. Such changes will require new regulatory approvals for the established products and may even result in alterations of the characteristics of the established products.
WO 2007/066017 describes a method for the production of Factor H preparations from cryo-poor plasma. Cryo-poor plasma, however, is a common source material for the manufacture of many commercially important IgG therapeutics, such as GAMMAGARD® LIQUID (Baxter Healthcare Corporation). WO 2007/06617 provides no guidance as to how the disclosed method, which involves passing cryo-poor plasma through at least two chromatographic steps, including anion exchange chromatography and heparin affinity chromatography, would impact, or even allow for, the manufacture IgG from the pre-processed cryo-poor plasma. In addition to requiring a complete revalidation and possible redesign of key IgG manufacturing processes, regulatory re-approval of the manufacturing procedures from key regulatory agencies would be required.
Likewise, WO 2008/113589 describes methods for the production of Factor H preparations from known plasma fractionation intermediates, namely Cohn-Oncley Fraction I supernatant, Cohn-Oncley Fraction II+III precipitate, and Kistler/Nitschmann Precipitate B fractions. Because these fractions are intermediates used in many commercially important IgG therapeutics, such as GAMMAGARD® LIQUID, implementation of these methods would likewise greatly impact existing IgG manufacturing capabilities.
U.S. Pat. No. 8,304,524 discloses methods for the isolation of Factor H from commonly produced by-products of IgG manufacturing processes, including Cohn Fraction I precipitate and Fraction II+III precipitate insoluble materials which are normally discarded. The '524 patent reports that about 90% of the Factor H content of plasma is fractionated into Cohn Fraction II+III precipitate during IgG manufacturing, and proposes that Factor H manufacturing efforts be focused on the extraction of Factor H from this by-product. However, Fraction II+III precipitate, and specifically the insoluble material derived therefrom and used in the '534 patent for the isolation of Factor H, contains high levels of proteolytic/amidolytic activity. It is shown herein that Factor H purified from Fraction II+III precipitate according to the methods of the '524 patent is proteolytically clipped to a large extent.
Brandstätter et al. (Vox Sanguinis (2012) 103, 201-212) report the purification of Factor H from an undisclosed plasma fraction. As in the '524 patent, Brandstätter et al. observe a large fraction of proteolytically clipped Factor H in their starting plasma fraction (see, lane 1 of the western blot shown in FIG. 3(b)).
Concerns over the amidolytic activity content of immunoglobulin compositions fueled by occurrences of thromboembolic events in patients being administered plasma-derived immunoglobulins and the recent withdrawal of two plasma-derived immunoglobulin compositions from market have highlighted a need for methods of effectively reducing serine proteases (e.g., activated protein C, kallikreins, FXIa, and FXIIa) during the manufacturing of plasma-derived therapeutics. Moreover, several studies have suggested that administration of high levels of amidolytic activity may result in unwanted thromboembolic events (Wolberg A S et al., Coagulation factor XI is a contaminant in intravenous immunoglobulin preparations. Am J Hematol 2000; 65:30-34; and Alving B M et al., Contact-activated factors: contaminants of immunoglobulin preparations with coagulant and vasoactive properties. J Lab Clin Med 1980; 96:334-346).
Thus, a need remains for methods of manufacturing plasma-derived Factor H compositions with reduced proteolytic profiles from the existing supply of plasma donations. Advantageously, the present disclosure fulfills these and other needs by providing improved methods that reduce the proteolytic content (e.g., amidolytic activity) of Factor H compositions prepared from precipitation byproducts normally discarded during the manufacture of commercial IgG therapeutic products.